[KevinH]

So not sure if this is a bug or not as there were no valid file extensions to begin with, which the current regex renamer code expects. We might have to modify the renamer code to compare the extracted file extension to a list of known valid file extensions, and then handle the case of invalid file extensions in some other way.

That might work. But doing the rename in 2 passes (as described above) should do the trick.